Metal Enhancement

Question 1

Heat treatment

Answer 1

Processes that enhance the properties of a metal through controlled heating and cooling

Question 2

Work hardening

Answer 2

‘Cold working’ the metal such as bending, rolling or hammering

Crystals within the metal are distorted and changed leading to improved hardness and tensile strength in the worked area

Distorted metal crystals can’t move freely within the metal structure, decreasing ductility, cracking or damage in the worked area

These effects can be removed via annealing

Question 3

Annealing

Answer 3

Used to make the work-hardened metal easier to work with by reducing brittleness and increasing ductility

Metal is heated and cooled very slowly, allowing metal crystals to grow and slowly move into place

Question 4

Case hardening

Answer 4

Used for hardening the surface of steels with less than 0.4% carbon content

Produces an outer casing of greater hardness, improved wear resistance and greater resistance to surface indentation whilst metal’s core remains ‘softer’.

Two stages:

1 - carburising
2 - quenching

Question 5

Case hardening - carburising

Answer 5

Changes the chemical composition of the steel’s surface

Steel is placed in ceramic box that is packed with carbon

Box is heated to 930-950 degrees, allowing carbon atoms to diffuse into the steel’s structure - builds up surface carbon content

The depth of carbon layer is determined by the length of time the material is exposed to the carbon

Longer time = thicker carbon layer

Product is then heated to 760 degrees and then quenched

Question 6

Case hardening - quenching

Answer 6

Quenching is the rapid cooling of a heat treated metal

Hot metal is dipped into water to cool it quickly and seal the hard surface case whilst not affecting the properties of the inner core

Question 7

Hardening

Answer 7

Medium and high carbon steels are heated to alter their crystalline structure, holding them at this temperature for a set duration. Then the steels are quenched in water, oil or salt-water baths

Increase hardness but also increase brittleness

Question 8

Tempering

Answer 8

Reduces some of the excess hardness and brittleness of a hardened metal

Increases toughness and ductility

Metal is heated to below the critical point for a given time then slowly air cooled

Temperature determines the amount of hardness removed

Tempering colour indicates the temperature at which brittleness is removed

Question 9

Metal enhancement processes

Answer 9

Work hardening

Annealing

Case hardening

Hardening

Tempering

Quenching